1. Technical Field
The present invention relates to disk drives in general, and in particular to a method for controlling disk accesses within a disk drive. Still more particularly, the present invention relates to a method and apparatus for detecting a position of an access mechanism and Making the access mechanism follow a target position of a disk within a disk drive.
2. Description of the Prior Art
A hard disk drive includes at least one disk, a voice coil motor (VCM), an access mechanism having a data read/write head located at an end of an access arm and being driven along the radial direction of a disk by the VCM, and a servo means for detecting a displacement of the access mechanism from a target position via a read signal of positional information (servo information) previously recorded on a disk surface, and making the access mechanism be positioned at and follow the target position in a target track.
For a hard disk drive having a sector servo system, data fields and servo fields are alternately arranged in the longitudinal direction of a track of a disk. In addition, a servo means of the sector servo system discretely detects a displacement of an access mechanism from a target position, controls the driving current of VCM on the basis of the displacement sampled, and makes the access mechanism follow the target position. A time interval of the above-described sampling is determined by a metric interval between servo fields in a track and the disk rotation speed.
There is a tendency for increasing the density of data storage in hard disk drives. The track width typically becomes narrower in order to increase the data storage density. As the track width becomes narrower, the tolerance to a deviation of an access mechanism from a target position during track following also decreases. Although it is necessary to shorten a sampling time interval of a displacement from the target position in order to reduce the influence of disturbance applied to an access mechanism, it is also necessary to store as much servo information on a disk surface as possible. As a result, the space of data fields on a disk that a user can use becomes smaller.
Consequently, it would be desirable to provide a method and apparatus that can reduce the influence of disturbance applied to an access mechanism and increase follow-up precision to a target position.
In accordance with a preferred embodiment of the present invention, a servo apparatus comprises a first detection means for discretely detecting a displacement value of an access mechanism from a target position at predetermined time intervals, a first feedback means for calculating a first feedback value on the basis of the detected displacement value, a second detection means for discretely detecting a physical value, including the speed of the access mechanism, at least once at each of the predetermined time intervals, a second feedback means for calculating a second feedback value on the basis of the physical value, including the speed, and a motor driving means for driving a motor according to the first feedback value and the second feedback value.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.